1. Field of the Invention
This invention relates to a navigation apparatus for vehicles and, more particularly, to a vehicle-mounted navigation apparatus which performed is error correction of an azimuth sensor which constitutes an input section for an independent navigation signal.
2. Description of the Prior Art
Currently, a navigation apparatus in accordance with a Global Positioning System (GPS) is quite effective for locating positions of various crafts such as sea vessels, aircraft and automobiles and has become popular. Such a navigation apparatus can determine or confirm vehicle's present position, traveling speed, and the like by receiving satellite signals transmitted by a plurality of artificial satellites. The Global Positioning System (GPS) is a kind type of satellite-based radio navigation system developed to determine the present position of a moving vehicle by receiving satellite signals from a plurality of artificial satellites known as GPS satellites.
As is well known, the positioning operation to be implemented by the GPS positioning apparatus is normally performed by receiving satellite signals transmitted from three or more GPS satellites. To determine the present position of the moving vehicle, the satellite signals transmitted by the plurality of GPS satellite are received simultaneously by a GPS receiver mounted on the moving vehicle such as a motor vehicle, and thereby a distance from each satellite is measured based on a time difference between clocks mounted on the motor vehicle and each of the GPS satellites.
Further, as a prior-art-type navigation apparatus, an independent or so-called self-determining type positioning apparatus is known for use by the motor vehicles. The self-determining type positioning apparatus is so arranged, different from the aforementioned GPS type navigation apparatus, as to determine its own present position based on data obtained independently without relying upon other data fed by any external units such as from the artificial satellites.
In accordance with the prior-art-type motor vehicle-mounted navigation apparatus, an earth magnetism sensor is employed as an azimuth sensor which constitutes a part of input sections for an independent navigation signal, however, there may cause a phenomenon of magnetization depending on a magnetic environment, this in turn results in problems such as introducing an error into the calculated present position of the motor vehicle.
It is therefore an object of this invention to eliminate the problems encountered by the prior-art-type navigation systems and to provide a motor vehicle-mounted navigation apparatus wherein error corrections for an azimuth sensor are implemented by feeding back an output signal of a control unit.